It is known that a person's physiology and wellbeing can be influenced by phototherapy. In particular, the production of melatonin, which increases during darkness, can be reduced by the influence of light. Melatonin is a hormone that makes a person sleepy. Hence a relatively long period of darkness causes tiredness. Recent research shows that there is a nonvisual photopigment in the eye, in the ganglial cells of the retina, which in phototherapy using relatively slight quantities of light causes suppression of melatonin production. The greatest biological effect is attained with blue light at a wavelength of approximately 464 nm. Incident radiation from a blue sky therefore is substantially more effective in suppressing melatonin production than artificial light from incandescent or fluorescent bulbs.
From German Patent Disclosure DE 102 32 797 A1, a device for enhancing vigilance of a driver of a vehicle is already known in which a source that emits electromagnetic waves is controlled as a function of the signals from a sensing device for detecting the degree of attentiveness on the part of the vehicle driver. The source that emits electromagnetic waves is either lights on the dashboard or the interior lighting of the vehicle. The known device has the disadvantage that the light source blinds the driver. This risk is especially high at night, because of course the surroundings of the driver and above all the road that the driver is supposed to observe is dark or only relatively weakly illuminated.